Category Archives: energy

The Energy Efficiency Project: Month 8

Energy Efficiency Project month 8

July 13th – August 13th, 31 days

Late July and early August was considerably drier in these parts, so we didn’t have to run our dehumidifier very often. With the dry also came the heat, however, so we definitely were running our ceiling fans for most of this month. On really hot afternoons when the fans just weren’t cutting it anymore I would close up the house and turn on the air conditioner. Once the house cooled down to about 74°F, I would turn off the AC and keep all the windows and doors shut to keep the heat from getting in as much as possible. Usually running the AC for an hour or so would cool down the house until the heat broke as the sun went down.

This month’s upgrade cost: $0.00

Total upgrade cost to date: $26.64

Over 31 days we used 492 KWH. Which comes out to an average 15.9 KWH/day. Compared to the last billing period average of 19.2 KWH/day, you can really see how much electricity that dehumidifier was using while it dried out our basement.

We are part of the Alliant Energy Second Nature renewable energy program, at the 100% level. (In this program you can choose the amount of your energy use that you want to be matched in renewables, and we chose 100%.) The cost of our renewable energy was $0.14 per KWH for this billing cycle, for a total of $69.81

This month we used 0 Therms of natural gas heat energy. Which averages out to 0.0 Therms/day. However we did still have a small charge to keep our gas on this month, and probably also to pay for meter readers and what not. Degree days this month compared to last month: 0 vs. 25

The natural gas market fluctuates in Wisconsin, so there is not an easy dollar per Therm number to give you, but during this billing period we paid $9.90 for our gas use.

Our energy bill also provides these numbers for helpful comparison:

Electricity used this month last year: 159 KWH. This was clearly the month that the previous owners moved out of this house and were just using maintenance electricity while it was on the market!

Gas used this month last year: Unavailable – Again, this is the time the previous owners moved out and put this house on the market, so they may have turned off the gas for the summer. Average temperature this month: 73° F. This month last year: 70° F.

Degree Days this month: 0 vs this month last year: 10. Degree days are the number of degrees below 65° F in one day, all added together for the total 31 days of the billing period.

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Want to see previous months of the Energy Efficiency Project? Here is Month 1Month 2, Month 3Month 4Month 5, Month 6, and Month 7.

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40 Green Actions You Can Start Today

simple green actions to start todayFor the past month I’ve had the opportunity to be a part of a climate change discussion group in my community. We’ve been reading EAARTH, and discussing the realities of climate change both world wide and within our own small part of SW Wisconsin. And we’ve been trying to envision what action looks like for us.

It’s easy to get overwhelmed by how big this problem is, and how little it seems like our personal actions are. The Tanzanian’s have a saying, “Haba na haba hujaza kibaba.” Which translates to “Little by little the bucket gets filled,” and that’s important for us to keep in mind. Yes, we may have seemingly little say in the policies enacted within our own states and country, let alone in the worldwide cooperation that is needed to tackle our energy, and resource issues and our greenhouse gas emissions. But we can start taking simple, concrete actions now. And as we successfully implement each habit, it will be easier to take the next step. Little by little, we’ll fill the bucket.

So with those thoughts in mind, here’s a list of actions you can start taking right now to increase conservation, decrease energy use, and reduce your carbon footprint.

40 green actions you can start today

1. Switch out your incandescent light bulbs for LED light bulbs.

2. Plug your electronics into a power strip, and turn off the power strip when you’re not using them.

3. Turn your thermostat up a few degrees now (and down a few degrees in the winter).

4. Sign up for your local power companies green energy program, you’ll pay a little extra for your energy, but you’ll get it from renewable supplies and tell your power company how important it is for them to invest in renewables.

5. Set the temperature on your hot water heater to 120 degrees or lower.

6. Hang dry your laundry.

7. Stop watering your grass.

8. Plant something edible.

9. Shop your local farmers market.

10. Bring reusable bags along for all your shopping trips (not just to the grocery store!)

11. Purchase dry goods like beans, grains, and pasta from the bulk bins.

12. Start a compost pile.

13. Clean with vinegar, baking soda, and castile soap.

14. Walk if your destination is less than a mile away. Work your way up to two miles away.

15. Look for opportunities to carpool or take public transportation.

16. Add meat-free meals to your repertoire.

17. Purchase humanely and ethically raised meat.

18. Unsubscribe from catalogs

19. Unsubscribe from “junk” mailings

20. Refresh yourself on your communities recycling capabilities and look for opportunities to expand your recycled materials.

21. Carry a reusable water bottle or coffee mug.

22. Use reusable bags or glasses for food storage.

23. Eat fruits and vegetables that are in season and grown in your area.

24. Support local small businesses and local trades workers.

25. Shop consignment or second hand stores for clothing, rather than buying new.

26. Share infrequently used appliances and tools with your neighbors, like lawn mowers.

27. Shovel your snow instead of using a snow blower.

28. Set up a clothing swap among your friends and neighbors.

29. Support local conservation by visiting your state parks.

30. Let your grass grow a bit longer between mowings.

31. Purchase “made in America” and recycled materials.

32. Donate your own no longer used items to second hand stores.

33. Cook more meals at home.

34. Make your own coffee.

35. Use mulch on your garden to cut down on watering needs.

36. Wash your clothing on the cold cycle.

37. Switch from paper napkins, towels, and tissue to cloth.

38. Check out books from the library.

39. Sign up for electronic statements.

40. Sign up for electronic bill pay.

Again, these simple actions aren’t going to save the world from climate change, but they will start a habit of mindfulness about consumption and energy use. These small actions can help pave the way for you to start taking bigger actions, and they can start conversations with your neighbors, friends, family, and co-workers.

Do you have others to add to this list? Send them my way!

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Home Solar Power: How much solar power do I need?

A few weeks ago I wrote about getting started with a home solar power project. That post was an overview on how much power you might need to power your home, and how much a home solar power project is likely to cost you. This week I’m going to start the deep dive, and I’ll use our home as an example.

How much solar power do I need

So, how much solar power do I need?

Well, let’s start with a quick overview of our household, so you can do a simple comparison to your own home and get an idea of if you’ll need more or less before doing your own deep dive.

Our house is a single story bungalow, a little over 1000 square feet. It is home to my husband Neil, our toddler Eli, and myself. We live in a small town in Wisconsin, so we have both cold winters, and fairly warm, humid summers. We are careful with our energy use, but we enjoy pretty much all modern amenities, with the exception of a dishwasher and a microwave. Our appliances are aging, 15 – 20 years is my guess, and we have an electric stove.

We are connected to the grid, and if we put in solar power here, we would stay connected to the grid.

Step 1: Calculate your energy use

Look up the amount of Kwh of electricity that you have used for each billing cycle over the past year. Add it all together, and divide by 365 (or 366 if it was a leap year).

You might think that you should look at your highest energy use month and use that to find your daily use. This method would help ensure that you are drawing all your energy from solar power all year long, but it is also going to cause the size of your solar project to go up quite a bit. This can be both cost and space prohibitive.

By building a solar power project based on energy use averaged over the entire year, you will probably have to buy some extra electricity during the winter, when there is less sunshine and you are possibly using more electricity. But in the summer, you will produce enough to sell back to the grid, recouping your electricity costs in the winter, and over time your solar power project costs. It will also keep your solar panel array to a more manageable size and cost.

Realistically, if you live in a city or town, you’re just not going to have the space necessary to put in enough solar power to meet your entire usage needs. But knowing how much you are using daily will put your project in scope from the beginning, and maybe also help you to think about where you could start cutting back. Remember, if you don’t use the energy in the first place you don’t have to pay for it, and we don’t have to create it by any means, saving all sorts of resources.

OK, so on to our house and our energy use. For the 7 months that we’ve been home owners thus far, I’ve been chronicling our energy use in the energy efficiency project posts. So far we’ve used 2873 Kwh over 208 days. This puts our average daily use at 13.8 Kwh. This is actually a pretty low ball estimate of our daily electricity use, because keep in mind that we were only living here part time for 5 of those months. As we continue living in this house, I’ll revisit these numbers and update as we get a more realistic idea of our average daily use.

Ok. So our goal is to produce 13.8 Kwh of electricity each day with our future solar panels.

Step 2: Find the amount of sun hours your location gets

We use 13.8 kwh of electricity each day, on average. But we don’t need to produce all that electricity at once, just over the course of the day. Because, as I’m sure you’re well aware, the sun doesn’t shine for just one hour most days. In the summer, it might be shining for 14 – 16 hours per day, and with solar panels you can turn that sunlight into electricity the entire time it’s shining. But, as I’m also sure you’re well aware, sometimes the sun really does only peak out for a short while, and some days not at all. So you need to find the average amount of time that the sun shines in your location each day.

Most companies that sell solar panels and accessories have charts and maps that can help you figure our the average hours of sunshine your location gets per day. For example, this chart on the Wholesale Solar website tells me that Madison, WI gets an average of 4.3 hours of sunlight each day. Again, this number is averaged over the entire year, so using it in my calculations means that on cloudy winter days, I’ll probably have to purchase electricity from the grid. But on sunny summer days, I’ll produce extra electricity that I’ll be able to sell back to my power company.

Step 3: Calculate the amount of solar power capacity you need. 

Solar power capacity is the amount of kilowatts your panel array can produce when the sun is shining on it at any moment. It’s pretty simple to calculate: Take your average daily electricity use, and divide it by the average daily hours of sunlight in your area.

For us, 13.8 kwh / 4.3 hours = 3.2 kilowatts.

So we want enough solar panels to produce 3.2 kilowatts of electricity.

Step 4: Factor in efficiency

You may remember from high school physics (or maybe not) that when energy is converted from one form to another, their are losses. In this case, when the light energy from the sun is converted into electrical energy by the solar panels, not all of the solar energy collected gets turned into electricity. Some of it is lost as heat, or friction between the electrons in the wires, etc. Currently, solar panels are 78% efficient. Meaning that 78% of the solar energy they collect, makes it into electricity.

In order to account for this efficiency (or inefficiency, as the case may be) we divide our solar power capacity by 0.78.

So, how much solar power do I need? 3.2 Kw * 0.78 = 4.1 Kw

In order to power our home we need enough panels to produce 4.1 Kw of electricity. How about you?

Or at least in an ideal situation. Next time we’ll take a look at other things we need to consider.

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Want to learn more about solar power? Check out how it’s made in these posts: Solar Power part 1, Solar Power part 2

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The Energy Efficiency Project: Month 7

energy efficiency project June 11th – July 13th, 32 days

We had a wet June and beginning of July in SW Wisconsin. Which led us to discover that are gutters are sagging in the front of our house, and therefore not directing the water to the downspout, but instead it’s basically just spilling right out in streams along the front of our house whenever it rains. And all that water coming down right along the front foundation of our house has left us with a soggy basement.

Ah, the joys of home ownership.

So to start battling the soggy basement we got a dehumidifier. And it does a decent job of drying out our basement, but it’s quite the little electricity suck, as you will see.

But I did replace yet another CFL lightbulb with an LED lightbulb. Progress?

This month’s upgrade cost: $8.82

Total upgrade cost to date: $26.64

Over 32 days we used 613 KWH. Which comes out to an average 19.2 KWH/day. Compared to the last billing period average of 13.4 KWH/day, you can really see how much electricity that dehumidifier was using while it dried out our basement. We also were making greater use of our ceiling fans, which also adds to our summer electricity use.

We are part of the Alliant Energy Second Nature renewable energy program, at the 100% level. (In this program you can choose the amount of your energy use that you want to be matched in renewables, and we chose 100%.) The cost of our renewable energy was $0.14 per KWH for this billing cycle, for a total of $86.98

This month we used 0 Therms of natural gas heat energy. Which averages out to 0.0 Therms/day. However we did still have a small charge to keep our gas on this month, and probably also to pay for meter readers and what not. Degree days this month compared to last month: 25 vs. 148

The natural gas market fluctuates in Wisconsin, so there is not an easy dollar per Therm number to give you, but during this billing period we paid $10.53 for our gas use.

Our energy bill also provides these numbers for helpful comparison:

Electricity used this month last year: 735 KWH. I find it comforting that even with our spike in electricity use this month, we’re still maintaining less energy use than the previous owners. This is purely speculation, because I don’t know what their habits were, but I think this is due to the fact that we almost never use the drier, we use fans and open windows rather than the air conditioning, and I have a hunch they were running a small business from home, so I think we also use less electronics than they did.

Gas used this month last year: Unavailable – I think this is about the time the previous owners moved out and put this house on the market, so they may have turned off the gas for the summer. Average temperature this month: 68° F. This month last year: 71° F.

Degree Days this month: 25 vs this month last year: 6. Degree days are the number of degrees below 65° F in one day, all added together for the total 32 days of the billing period.

Have you signed up for the building earth newsletter yet? You can do that here!

Want to see previous months of the Energy Efficiency Project? Here is Month 1Month 2, Month 3Month 4Month 5, and Month 6.

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Home Solar Power: Getting Started

home solar powerA couple weekends ago I had to opportunity to attend a class entitled “Do It Yourself Photovoltaics” which was put on through our local garden center. The man who taught the class, Mr. Jon Passi, stressed that his goal was to make solar power projects as accessible as possible to others, and encouraged us to share what we learned from his class with our neighbors, so I’d like to share a bit about what I learned with you.

home solar panels 3

How Much Solar Power Do You Need

The first step to getting a home solar project going is to figure out how much power you need. Most power companies these days will provide graphs of your power use for the past year, so you can see how much electricity you use each month. When you look at this graph you’ll probably see that you have a season of the year where you use quite a bit of electricity, and a season where you use less. For my family, we use more electricity in the winter time than the summer, because we are more likely to be inside, and because it is dark during more of our waking hours. But if you might find that the opposite is true for you, depending on your habits and your home.

So, take a look at your energy use over the course of a year. With solar power, you produce the amount of electricity you use each day, and then start over again the next day. Figure out what your average monthly electricity use is. Then divide that number by 30 to get an estimate of your average daily electricity use. For the average American family, this number is somewhere in the range of 20 – 40 Kwh per day.

Your average daily electricity use is what you’re shooting to produce with a home solar power project. Yes, some days you will use more, but if you’re still connected to the power grid, you’ll be able to draw whatever extra you need from your power company. And on other days you will use less electricity than the average, and on those days you will be able to sell back any extra that you produce to the power company. It will all even out in the end, and usually in your favor – depending on your power company, you’ll be able to sell your extra electricity to the power company for more than you are paying for the little bit you need from them on cloudy days or days when your energy use is a bit higher than average.

home solar panels 2

How Much Will Home Solar Power Cost

The next step is to figure out if you can lower this number. Home solar projects are still pretty expensive, so the more you can lower your daily needs, the less you need to invest in supplying that power. Before you start shelling out dollars for solar panels, maybe it’s the right time to upgrade to a more energy efficient refrigerator, dish washer, or washer and drier. Maybe it’s time to commit to hang drying your clothes. Make sure your computer, television, and gaming systems are all on power strips that you turn off when you’re not using them to reduce the amount of phantom load your electronics are drawing. Upgrade your lightbulbs to LEDs. Before you spend $10k+ on solar panels, spend a couple months committing to lowering your energy use, and then recalculate your average daily electricity use.

A good rule of thumb right now for how much a home solar power project is going to cost you is to multiply your average daily electricity use by 1000. So if your home uses 22 Kwh of electricity per day, the cost of a project big enough to cover your entire energy needs would be about $22,000.

Before you get bug eyed at the cost of a home photovoltaic project, keep in mind that there are currently lots of opportunities for energy rebates. The federal government will give you 30% of the cost of the project in rolling tax breaks. (Rolling means that if you don’t use the whole 30% the first year, you can take the remainder the following years until you reach the full 30%.) Many power companies are also offering rebates for home solar projects right now as well. Mr. Passi gave us some examples of projects that he worked on in the past couple years, and many times the after rebate costs were around 60% of the total cost of the project.

Also, keep in mind that solar panels take up quite a bit of space. You likely won’t have enough room on your roof (especially in a city or suburb situation) to even install enough solar to cover the entirety of your daily use. When you look at how much solar power you can actually install on your house, the scope of your home solar power project may drop significantly. And even if you’re only supplying some of your home electricity needs, on sunny summer days, you will likely still produce quite a bit of extra electricity to sell back to the grid.

I have plenty more to share on this topic, but I think this is a good start for today. In the future I’ll get into more about the components you need for a home solar power project, and use our house as an example for figuring out how much electricity you need to produce and the costs of completing that project.

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The Energy Efficiency Project: Month 6

energy efficiency project month 6May 13th – June 11th, 29 days

We are finally maintaining only one residence. Let me tell you, as convenient as it was to have a place to stay in both of the cities that my husband works in for the past six months, two homes is hard. And expensive. Especially with only one home’s worth of stuff.

During that time, we of course also had two different utility bills, which was quite interesting. Each place was serviced by a different utility company, MG&E, and Alliant, but the offerings as far as renewable energy went were pretty much the same. Our apartment was about 500 square feet, and had electric baseboard heating. And let me tell you, our energy costs there were much higher than for our 1000 square foot house that has a gas furnace. It was surprising to me just how expensive and inefficient electric heating is. I’ll get more into that in a future post.

So now we have one home. One energy bill. And now the burden of maintenance is on us rather than a landlord. Time to get busy.

Again, nothing special in terms of upgrades for energy efficiency this month. We’re spending most of our time and energy this spring and summer on our yard and garden and all that outside stuff that it sure is nice to have warm weather to complete. But it’s important to have months where we don’t make any big changes and just live in our home so we can get a sense of our baseline energy use.

This month’s upgrade cost: $0

Total upgrade cost to date: $17.64

Over 29 days we used 390 KWH. Which comes out to an average 13.4 KWH/day. Compared to the last billing period average of 15.5 KWH/day, we dropped a bit, due to spending a week or so in our apartment getting ready to move out.

We are part of the Alliant Energy Second Nature renewable energy program, at the 100% level. (In this program you can choose the amount of your energy use that you want to be matched in renewables, and we chose 100%.) The cost of our renewable energy increased on June 1st, So the cost of our electricity is $0.13 per KWH for the 18 days of May on our bill, and $0.14 per KWH for the 11 days of June, for a total of $52.68.

This month we used 0 Therms of natural gas heat energy. Which averages out to 0.0 Therms/day. However we did still have a small charge to keep our gas on this month, and probably also to pay for meter readers and what not. Degree days this month compared to last month: 148 vs. 347.

The natural gas market fluctuates in Wisconsin, so there is not an easy dollar per Therm number to give you, but during this billing period we paid $8.93 for our gas use.

Our energy bill also provides these numbers for helpful comparison:

Electricity used this month last year: 758 KWH. I imagine this number is going to drop pretty significantly in coming months, because we’re almost to the point where the previous owners of the house listed it for sale, and during that time they were already living in a different residence.

Gas used this month last year: 1 Therm. Average temperature this month: 63° F. This month last year: 54° F.

Degree Days this month: 148 vs this month last year: 108. Degree days are the number of degrees below 65° F in one day, all added together for the total 29 days of the billing period.

Have you signed up for the building earth newsletter yet? You can do that here!

Want to see previous months of the Energy Efficiency Project? Here is Month 1Month 2, Month 3Month 4, and Month 5.

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3 Energy Wins to Celebrate this Fourth of July

Happy Birthday America!

While we celebrate our Independence this weekend, let’s also celebrate some of the wins we’ve made in America and around the world in the past year in terms of renewable energy growth.

3 energy wins to celebrate this fourth of july

Fireworks by Jeff Golden //CCBY

1. We’ve reached 1% of worldwide energy generation through solar power!

Ok, so 1% sounds pretty small, but nearly a quarter of that was installed just within the last year, and the prices on solar generation continue to fall, meaning that soon it will not only be the earth friendly way to get your electricity, but it will also be the wallet friendly way. This first 1% is hard won, requiring decades of work by scientists and engineers to bring the technology forward and the price down. China, Japan, and the U.S. are leading the way on solar power installation.  You can read more about this achievement here.

2. Dirty, Old coal plants are retiring across the U.S.

In the past year, 7% of coal plants have been retired. These retired plants are the oldest of the currently existing coal plants and dirtiest methods we currently have of generating electricity, so shutting them down is a good step to reducing the dangerous particulates they exhaust – like mercury, from the air. The old coal plants are retiring for a couple reasons – they are too dirty to meet current regulations, and they are being priced out by the plummeting costs of producing electricity using renewables.  You can read more about the shutting down of coal plants here.

3. We’re building battery capacity

One of the biggest challenges with the move to renewables such as wind and solar, is that the amount of energy that they generate fluctuates. On a windy day, wind turbines can be constantly generating electricity, but if the wind dies down – people will still want to use their computers, refrigerator, and air conditioning regardless. Same with solar power, the power generation fluctuates not only with day and night, but with cloud levels and season. A sunny day in Arizona can produce more energy collected by solar panels than all the people of Arizona can use in a day, but at night, that all goes away. So battery capacity is key for capturing and saving all that energy until it is needed. This means that projects like the Tesla Gigafactory will be key in meeting our energy storage needs.  You can read more about the Tesla Gigafactory here.

So there you have it, while you are celebrating independence this weekend, go ahead and light a sparkler or two for these 3 energy wins to celebrate this year.

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The Energy Efficiency Project: Month 5

I’m back after a couple week hiatus due to finally finishing up our move from apartment to house, some traveling, and some adjusting to a new schedule. One of the troubles with having a significant other who is in residency is the constantly shifting schedules. Throw in the mix a toddler that thrives on a schedule, and it means our life sometimes goes topsy-turvy as we adjust. And now we’re well past due for giving you an energy efficiency project update. So, here goes.

energy efficiency project month 5

April 14th – May 13th, 29 days

We had a mid-April cold snap that caused us to turn the heat back on for a week or so. And as I mentioned above, we completed our move during this billing period, so we have a few more energy users in our home these days – a television and XBox, a lamp, etc. And lengthening days mean we’re using our lights less. Nothing special in terms of upgrades for energy efficiency this month. But it’s important to have months where we don’t make any big changes and just live in our home so we can get a sense of our baseline energy use.

This month’s upgrade cost: $0

Total upgrade cost to date: $17.64

Over 29 days we used 451 KWH. Which comes out to an average 15.5 KWH/day. Compared to the last billing period average of 9.45 KWH/day, you can see the definite difference in energy use between basic maintenance mode, and everyday living mode.

We are part of the Alliant Energy Second Nature renewable energy program, at the 100% level. (In this program you can choose the amount of your energy use that you want to be matched in renewables, and we chose 100%.) So the cost of our electricity is $0.13 per KWH, for a total of $59.04.

We also used 13 Therms of natural gas heat energy. Which averages out to 0.45 Therms/day. Huzzah for spring and only using our furnace for about a week during this month. Degree days this month compared to last month: 347 vs. 754.

The natural gas market fluctuates in Wisconsin, so there is not an easy dollar per Therm number to give you, but during this billing period we paid $15.45 for our gas use.

Our energy bill also provides these numbers for helpful comparison:

Electricity used this month last year: 740 KWH

Gas used this month last year: 17 Therms. Average temperature this month: 53° F. This month last year: 51° F.

Degree Days this month: 347 vs this month last year: 466. Degree days are the number of degrees below 65° F in one day, all added together for the total 33 days of the billing period.

Want to see previous months of the Energy Efficiency Project? Here is Month 1Month 2, Month 3, and Month 4.

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The Energy Efficiency Project: Month 4

Energy Efficiency Project Month 4March 12th – April 14th, 33 days

This month was pretty boring as far as energy efficiency improvements go. We turned off the heat at the beginning of April and got to start working on the yard a bit. We were still splitting our time between the house and our apartment in the city during this month, so the house was using minimal maintenance energy while we weren’t in it. For example, the furnace was set just high enough to keep our pipes from freezing while out of the house, and really only the fridge was using electricity most of the time. So, again, this month won’t be the best representation of our energy use, but will hopefully serve as a good reminder to put your house into low-energy-use mode when you’re gone for extended periods of time. As far as energy efficiency initiatives went we:

  • Turned off thermostat starting on April 1st!
  • Made sure that all lights and other electricity users aside from the refrigerator were off while we were away.

This month’s upgrade cost: $0

Total upgrade cost to date: $17.64

Over 33 days we used 312 KWH. Which comes out to an average of 9.45 KWH/day. Which is a small decrease from the last billing period average of 10.75 KWH/day. My guess is our decrease came from extended daylight hours, which meant less lightbulb use while we were in the house.

We are part of the Alliant Energy Second Nature renewable energy program, at the 100% level. (In this program you can choose the amount of your energy use that you want to be matched in renewables, and we chose 100%.) So the cost of our electricity is $0.13 per KWH, for a total of $40.85.

We also used 35 Therms of natural gas heat energy. Which averages out to 1.06 Therms/day. We only used the gas furnace for the first half of this billing month, and then of course had some gas use for the hot water heater. Also, we had a pretty warm start to our spring in these parts, so the degree days this month compared to last month: 754 vs. 1383. As you can see, the degree days this month is only a bit more than half of last month, which explains why we were able to turn off our furnace completely for half the month.

The natural gas market fluctuates in Wisconsin, so there is not an easy dollar per Therm number to give you, but during this billing period we paid $32.24 for our gas use.

Our energy bill also provides these numbers for helpful comparison:

Electricity used this month last year: 651 KWH

Gas used this month last year: 41 Therms. Average temperature this month: 43° F. This month last year: 36° F.

Degree Days this month: 754 vs this month last year: 835. Degree days are the number of degrees below 65° F in one day, all added together for the total 33 days of the billing period.

Want to see previous months of the Energy Efficiency Project? Here is Month 1Month 2, and Month 3

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Adding Insulation for Energy Efficiency part 2

The last time we checked in on the topic of insulation and insulating a house to the point where it wouldn’t need a furnace was back in December. Sheesh. The cold has broke here in the northern great lakes region, and while there is still a chill in the air some days, we seem to be headed right into spring. The good news is, insulation is not just a winter topic. Good insulation in your home will help keep it comfortable all year long. And keep your energy bills down. And so we forge ahead with adding insulation for energy efficiency.

Previously, I walked through the calculations to determine the payback period for adding insulation. Today let’s look at a couple of examples of how that might work our in practice.

  • R-value of the initial insulation (Ri)
  • R-value of the final insulation (Rf)
  • Cost of insulation (Ci)
  • Efficiency of the heat system (E)
  • Cost of energy (Ce)
  • Number of Heat Degree Days for the year (HDD)

And the equation looks like this:

P = (Ci * Ri * Rf * E) / (Ce * (Rf – Ri) * HDD * 24)

OK, take a deep breath. We’re about to do some math!

Example 1: Fiberglass Insulation Upgrade

For our first example, we’ll use the following situation: A house in Wisconsin is going to have its insulation upgrades. It currently has fiberglass batting with an R-value of 13, and will be upgraded to fiberglass batting with an R-value of 19. The cost of the new insulation is $0.41 per square foot. The house is heated by a natural gas furnace that is 85% efficient. The cost of natural gas in Wisconsin is $0.82 per therm, and 1 therm is equal to 100,000 Btu (British thermal units). The number of heating degree days for Wisconsin is 7499. We want to find the payback period for the new insulation.

So, breaking down our equation, we have:

Ci = $0.41 per square foot

Ri = 13

Rf = 19

E = 85% = 0.85

Ce = $0.82 per therm = $0.0000082 per Btu

HDD = 7499

P = (0.41 * 13 * 19 * 0.85) / ((0.0000082) * (19 – 13) * 7499 * 24)

P = 9.7 years

Wowza! That’s more time than I was expecting. So what are the key factors here that could cause this to payback period to go down? Well, first of all, with a little more looking, you might be able to find a better price on your insulation than a quick tour through the Home Depot website gave me. Also, natural gas in Wisconsin is pretty dang cheap right now, all things considered. But as more cities and states do things like ban fracking for natural gas, that cost could go up significantly, which would obviously bring the payback period down.

Example 2: Sprayed Foam Insulation – How much can we get?

What if instead of replacing all that R-13 fiberglass insulation with R-19 fiberglass insulation, we wanted to replace it with spray foam insulation?

Spray foam insulation has an R-value per inch of foam thickness. You can increase the total R-value by spraying a thicker layer of foam. There are tons of options available as far as spray foam goes, but for the sake of this example, we will use this Dow Froth Pack as our insulation. This spray foam provides R-6 per inch of thickness, so 1 inch has R-6, 2 inches has R-12, 3 inches has R-18, so on and so forth.

In this example, instead of calculating the payback period for the spray foam insulation, we’re going to see how thick of an insulation layer we can “afford” to apply, given the same payback period as the upgrade from R-13 to R-19 fiberglass. In other words, we are going to solve for Rf.

So, breaking down our equation, we have:

Ci = $1.01 per square foot

Ri = 13

Rf = x

E = 85% = 0.85

Ce = $0.82 per therm = $0.0000082 per Btu

HDD = 7499

P = 9.7 years

Through the magic of algebra, we can rearrange our equation to solve for Rf:

Rf = (P * Ri) – P – ((Ci * Ri * E)/(Ce * HDD * 24))

Which looks gross, but it’s really just a matter of plug and chug at this point:

Rf = (9.7 * 13) – 9.7 – ((1.01 * 13 * 0.85)/(0.82 * 7499 * 24))

Rf = 10.67, or about 1.75 inches thickness of the spray foam insulation.

So, for the same payback period as with the fiberglass insulation, we’d actually be downgrading from R-13 to R-10.67 with the spray foam. If we wanted to increase to the equivalent R-value, our payback period with the spray foam would be nearly twice as long!

But then what’s all the fuss about spray foam insulation? Why would anyone use it if the return on investment is apparently so low? Well, the R-value of the insulation isn’t telling you the whole story here. Remember the walls of your house are not just made out of batts of insulation. There is also the framing, the siding, the sheet rock, and all the other layers to consider. And those layers typically have small cracks and crevices where the heat can leak quite easily. One of the benefits of the spray foam insulation is that it fills in and seals all those leaky spots. So not only do you have the impact of the insulation layer, but you’ve increased the insulation abilities of all those other layers as well. Insulation can be one of those things were whole is greater than the sum of the parts.

Onward, Energy Efficiency Warriors. Next time we visit this topic we’ll get to the big finale: Can you insulate a house enough such that you don’t need a furnace???

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